全文获取类型
收费全文 | 847篇 |
免费 | 12篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 7篇 |
化学工业 | 35篇 |
金属工艺 | 3篇 |
机械仪表 | 7篇 |
建筑科学 | 1篇 |
矿业工程 | 1篇 |
能源动力 | 6篇 |
轻工业 | 12篇 |
石油天然气 | 3篇 |
无线电 | 37篇 |
一般工业技术 | 51篇 |
冶金工业 | 647篇 |
原子能技术 | 4篇 |
自动化技术 | 46篇 |
出版年
2023年 | 3篇 |
2022年 | 3篇 |
2021年 | 2篇 |
2020年 | 1篇 |
2019年 | 5篇 |
2018年 | 3篇 |
2017年 | 2篇 |
2016年 | 5篇 |
2015年 | 6篇 |
2014年 | 11篇 |
2013年 | 33篇 |
2012年 | 5篇 |
2011年 | 14篇 |
2010年 | 11篇 |
2009年 | 13篇 |
2008年 | 9篇 |
2007年 | 6篇 |
2006年 | 4篇 |
2005年 | 1篇 |
2004年 | 5篇 |
2003年 | 9篇 |
2002年 | 2篇 |
2001年 | 2篇 |
2000年 | 6篇 |
1999年 | 24篇 |
1998年 | 201篇 |
1997年 | 127篇 |
1996年 | 87篇 |
1995年 | 48篇 |
1994年 | 30篇 |
1993年 | 37篇 |
1992年 | 15篇 |
1991年 | 31篇 |
1990年 | 13篇 |
1989年 | 13篇 |
1988年 | 17篇 |
1987年 | 10篇 |
1986年 | 12篇 |
1985年 | 8篇 |
1984年 | 1篇 |
1983年 | 4篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 3篇 |
1976年 | 14篇 |
排序方式: 共有860条查询结果,搜索用时 9 毫秒
81.
AR Padhani WW Scott M Cheema D Kearney YS Erozan 《Canadian Metallurgical Quarterly》1997,32(8):453-458
RATIONALE AND OBJECTIVES: The authors evaluate the role of immediate cytologic evaluation (ICE) with fine-needle aspiration biopsy (FNAB) for lung lesions at highest risk for pneumothorax. METHODS: A prospective randomized study was conducted of 80 patients with lung lesions surrounded by aerated parenchyma undergoing FNAB with and without ICE (47 and 33 patients, respectively). An analysis of needle passes, procedure time, complications, specimen adequacy, diagnostic yield, and accuracy of procedure was made. RESULTS: There was an increased number of needle passes with ICE (> or = three passes: 23% [11 biopsies] versus 3% [1 biopsy]; P = 0.01). Fluoroscopic procedures took longer with ICE (median time: 15 versus 9 minutes; P = 0.002) with no difference in complication rates. Specimen adequacy was similar (74% and 64%) and the procedure was diagnostic in 79% (37 biopsies) with ICE and in 70% (33 biopsies) without ICE. There were no significant differences in the sensitivity, specificity, or accuracy of the biopsy. CONCLUSIONS: Immediate cytologic evaluation improved results marginally with increased procedure time and needle passes. Immediate cytologic evaluation may be most useful for lesions at lowest risk of complications to assure that a second procedure is not required. 相似文献
82.
Preproenkephalin (PPE) gene expression is specifically induced by estrogen in hypothalamus of ovariectomized (OVX) females, better than in male rats. To study estrogen actions on gene regulation, we have presently characterized protein-DNA interactions by use of a consensus estrogen response element (ERE) and a putative ERE from PPE gene, with nuclear extracts from hypothalamus. By use of the electrophoretic mobility shift assay (EMSA), ERE binding activity was detected in nuclear extracts from neuronal tissues including hypothalamus, hippocampus, striatum, cerebellum and frontal cortex, and non-neuronal tissues such as pituitary and uterus, but not lung of OVX female rats with a consensus ERE, as well as a 129-bp PCR fragment from PPE promoter and a hairpin oligonucleotide that contains a putative ERE of the rat PPE gene. The ERE binding was eliminated by the addition of specific ERE-containing oligonucleotide, but not control oligonucleotides. Protein and DNA associated and dissociated very rapidly. By use of supershift assay, interactions of estrogen receptor with ERE were demonstrated in hypothalamic nuclear extracts. The initial levels of specific ERE binding in the hypothalamic nuclear extracts were comparable between castrated male and OVX female rats. However, estrogen treatment, either estradiol or estradiol benzoate, produced a rapid and tissue-specific induction of a slow mobility complex of ERE binding in hypothalamic nuclear extracts from females, better than in male rats, presumably from other associated factors, or a conformational change or other posttranslational modifications. This estrogen-induced slow mobility complex of ERE binding in hypothalamus was not observed after treatment with progesterone or tamoxifen. These results suggest that specific ERE binding is present in rat hypothalamic nuclear proteins, which may contribute to the upregulation of PPE gene expression by estrogen, and that the sexually differentiated action of estrogen may be related to an estrogen-induced conformational change, but not to the initial level of ERE-binding activity. 相似文献
83.
84.
The strength of the stress singularities at the apex of a sharp V-notch for plane problems are investigated analytically in this paper. Three sets of boundary conditions, namely, free-free, fixed-fixed, and fixed-free, along the two faces of the notch are considered. The material is assumed to be governed by the deformation theory of plasticity with linear hardening characteristic. Results for both plane stress and plane strain conditions are presented. 相似文献
85.
Brain acetylhydrolase that inactivates platelet-activating factor is a G-protein-like trimer 总被引:1,自引:0,他引:1
YS Ho L Swenson U Derewenda L Serre Y Wei Z Dauter M Hattori T Adachi J Aoki H Arai K Inoue ZS Derewenda 《Canadian Metallurgical Quarterly》1997,385(6611):89-93
The platelet-activating factor PAF (1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine) is a potent lipid first messenger active in general cell activation, fertilization, inflammatory and allergic reactions, asthma, HIV pathogenesis, carcinogenesis, and apoptosis. There is substantial evidence that PAF is involved in intracellular signalling, but the pathways are poorly understood. Inactivation of PAF is carried out by specific intra- and extracellular acetylhydrolases (PAF-AHs), a subfamily of phospholipases A2 that remove the sn-2 acetyl group. Mammalian brain contains at least three intracellular isoforms, of which PAF-AH(Ib) is the best characterized. This isoform contains a heterodimer of two homologous catalytic subunits alpha1 and alpha2, each of relative molecular mass 26K, and a non-catalytic 45K beta-subunit, a homologue of the beta-subunit of trimeric G proteins. We now report the crystal structure of the bovine alpha1 subunit of PAF-AH(Ib) at 1.7 A resolution in complex with a reaction product, acetate. The tertiary fold of this protein is closely reminiscent of that found in p21(ras) and other GTPases. The active site is made up of a trypsin-like triad of Ser 47, His 195 and Asp 192. Thus, the intact PAF-AH(Ib) molecule is an unusual G-protein-like (alpha1/alpha2)beta trimer. 相似文献
86.
87.
88.
Erosion-corrosion (EC) is a serious degradation mechanism of piping, especially for nuclear power plants since it may result in the piping damage, plant shutdown, or personnel injury. The majority of this paper investigates the dependence of wall thinning on the hydrodynamic characteristics using the computational fluid dynamics (CFD) methodology. Four piping systems in a pressurized water reactor (PWR) power plant are selected in this investigation. Based on the plots showing the measured wall thinning with the calculated hydrodynamic parameters, the relationship between them is clearly revealed. Utilizing the characteristics of near-wall turbulence kinetic energy, an envelopment model is proposed herein to conservatively predict the amount of wall thinning distributed on the pipe wall. This estimation model can simply predict the possible distributions of severe EC wear sites and subsequently assist the plant staff to schedule the pipe wall monitoring program in the measured range of pipe wall for the fittings. 相似文献
89.
90.
JM Benson IY Chang YS Cheng FF Hahn CH Kennedy EB Barr KR Maples MB Snipes 《Canadian Metallurgical Quarterly》1995,28(2):232-244
The goals of this study were to (1) determine the effects of repeated inhalation of relatively insoluble nickel oxide (NiO) and highly soluble nickel sulfate hexahydrate (NiSO4.6H2O) on lung particle clearance, (2) investigate the effects of repeated inhalation of NiO or NiSO4 on the pulmonary clearance of subsequently inhaled 85Sr-labeled microspheres, (3) correlate the observed effects on clearance with accumulated Ni lung burden and associated pathological changes in the lung, and (4) compare responses in F344 rats and B6C3F1 mice. Male F344/N rats and B6C3F1 mice were exposed whole-body to either NiO or NiSO4.6H2O 6 hr/day, 5 days/week for up to 6 months. NiO exposure concentrations were 0, 0.62, and 2.5 mg NiO/m3 for rats and 0, 1.25, and 5.0 mg NiO/m3 for mice. NiSO4.6H2O exposure concentrations were 0, 0.12, and 0.5 mg NiSO4.6H2O/m3 for rats and 0, 0.25, and 1.0 mg NiSO4.6H2O/m3 for mice. After 2 and 6 months of whole-body exposure, groups of rats and mice were acutely exposed nose-only to 63NiO (NiO-exposed animals only), 63NiSO4.6H2O (NiSO4.6H2O-exposed animals only), or to 85Sr-labeled polystyrene latex (PSL) microspheres (both NiO- and NiSO4.6H2O-exposed animals) to evaluate lung clearance. In addition, groups of rats and mice were euthanized after 2 and 6 months of exposure and at 2 and 4 months after the whole-body exposures were completed to evaluate histopathological changes in the left lung and to quantitate Ni in the right lung. Repeated inhalation of NiO results in accumulation of Ni in lungs of both rats and mice, but to a greater extent in lungs of rats. During the 4 months after the end of the whole-body exposures, some clearance of the accumulated Ni burden occurred from the lungs of rats and mice exposed to the lower, but not the higher NiO exposure concentrations. Clearance of acutely inhaled 63NiO was also impaired in both rats and mice, with the extent of impairment related to both exposure concentration and duration. However, the clearance of acutely inhaled 85Sr PSL microspheres was not impaired. The repeated inhalation of NiO resulted in alveolar macrophage (AM) hyperplasia with accumulation of NiO particles in both rats and mice, chronic alveolitis in rats, and interstitial pneumonia in mice. These lesions persisted throughout the 4-month recovery period after the NiO whole-body exposures were terminated. In contrast, repeated inhalation of NiSO4.6H2O did not result in accumulation of Ni in lungs of either rats or mice and did not affect the clearance of 63NiSO4.6H2O inhaled after either 2 or 6 months of NiSO4.6H2O exposure. Clearance of the 85Sr-labeled microspheres was significantly impaired only in rats exposed to the microspheres after 2 months of exposure to NiSO4.6H2O. Histopathological changes in rats were qualitatively similar to those seen in NiO-exposed rats. Only minimal histopathological changes were observed in NiSO4.6H2O-exposed mice. These results suggest that repeated inhalation of NiO at levels resulting in AM hyperplasia and alveolitis may impair clearance of subsequently inhaled NiO. The potential effects of repeated inhalation of soluble NiSO4.6H2O on the clearance of subsequently inhaled poorly soluble particles are less clear. 相似文献